جستجوی مقالات مرتبط با کلیدواژه "stream sediments" در نشریات گروه "زمین شناسی"

The study area is located in the south of Qushadagh mountain range, in the north of Asbkhan village, Heris township. In terms of structural geology of Iran, this area is located in the main zone of Central Iran and Alborz-Azerbaijan sub-zone. The geological units of the region are including Eocene igneous and pyroclastic rocks with combination of andesitic, trachyandesitic, basaltic, tuffic and ignembritic. The semi-deep intrusive mass with Oligocene age, with the combination of quartz diorite, diorite and quartz monzonite in the form of stock and dyke is exposed in the area. Under the influence of hydrothermal processes originating from this intrusive mass and infiltration of fluids through the sedimentary-volcanic units of the Middle Eocene, extensive alterations (sericitic, medium argillic, propylitic and siliceous) have been taken place in the region. Preliminary results of geochemical studies of stream in the region led to the identification of several areas with grade 1, 2 and 3 anomalies of heavy minerals. The most important heavy minerals identified, include hematite, goethite, magnetite, pyrite-oxide, pyrite and zircon, These minerals and have closely relation to the alteration zones and veins mineralization. The conformity of the geochemical halos map with the geostructure and alteration map of the region shows a very high correlation between these regions and possibly the important role of faults and joints in the occurrence of alteration zones and abnormal regions. Anomaly maps and geostatistical analyzes performed on the findings in stream sediments and heavy minerals show that the enrichment of Ag, Au, Mo, Cu, As, Pb, Sb and Zn elements is higher than the background and the Au, Ag, Cu, As and Pb elements can be used as trace elements for epithermal gold reserves.

In order to investigate the concentrations of heavy metals in stream sediments of the Baycheh-Bagh area, northwest of Zanjan province, 131 samples were collected from intended stations. These samples after dissolution by four acid method, were analyzed by ICP-OES. To determine the type of spatial distribution of data, two important spatial statistics, i.e. global Moran’s I and Anselin local Moran’s I were employed. The average concentrations of As, Bi, Cd, Ni, Pb, Sb and Cu in stream sediment samples were 21.83, 0.32, 0.35, 35.57, 68.96, 37.67, 1.96 and 82.71 ppm, respectively which are higher than the average of crust whereas the average concentration of Co is 20.30 ppm. The obtained results indicate that the heavy metals in the study area has a spatial structure and distributed in cluster form.According to the Local Moran’s I results, the most contaminated area in the study area was detected in western part of the Baycheh-Bagh abounded mine and located on the present polymetallic vein-veinlet mineralizations and their related alterations. Analysis of obtained data and investigation of their relationship with the geological rock units of the study area show that concentration of the studied elements have geogenic source and is related to the mineralizations and alterations.

Heavy metals are one of the most important sediment contaminations and are important in low concentrations due to their in solubility and their physiological effects on organisms and human (Zare Khosh Eghbal et al. 2012). In an aqueous environment, sediments are the final destination of heavy metals accumulation and can act as a source of water pollution. On the other hand, mineral resources, especially metal deposits, contain significant amounts of heavy metals and potentially toxic elements. Contact of surface and underground water with the host rocks, ore mineralizations and altered rocks releases various elements, provides a large amount of heavy metals and potentially toxic elements in downstream deposits and surrounded soils. This fact highlights the importance of environmental studies of stream sediments. Spatial statistics is one of the basic concepts of modern sciences in monitoring and analyzing environmental data that focuses on the spatial relationship of data.
Spatial analysis of environmental data is crucial factor in spatial statistics. The first step in spatial analysis is identifying the data dispersal structure. Regarding to the importance of monitoring the spatial changes of environmental data and considering the distribution, arrangement and behavior patterns of variables in environmental topics, this study attempts to investigate the pattern of heavy metals dispersion in the stream sediments of the Baycheh-Bagh area, located in the northwest of Zanjan.

In order to evaluate the environmental contamination of heavy metals in the Baycheh-Bagh area, 131 samples were selected from intended stations. In this step, about 500 gr of stream sediments from a depth of 5-15 cm was selected from each station. After crushing and milling the samples, the obtained powders were dissolved by the four acid solutions and were analyzed by the ICP-OES at Environmental Science Research Laboratory, University of Zanjan. The studied elements in this research include As, Sb, Cd, Pb, Zn, Ni, Co, Bi and Cu. After receiving the analytical results from the laboratory, the data were processed statistically. For this purpose, the statistical parameters such as mean, median, mod, standard deviation, skewness, Kurtosis, range, minimum and maximum were analyzed for the nine mentioned elements using SPSS 22 software. Furthermore, Kolmogorov-Smirnov test was used to examine the distribution of the normal data. In the absence of normal data, the logarithm transformation method was used to normalizing them. To determine the amount of stream sediments contamination to heavy elements in the study area, global Moran’s I and Anselin local Moran’s I were employed. Determination of the degree of dispersion or clustering of features, global Moran’s I was used.
 

  The Global Morans’s I spatial autocorrelation was used to determine the spatial distribution of the data. The results of this analysis indicate that all metals have a strong correlation and cluster distribution. The Moron index for all metals is above 0.9 and among them the strongest and weakest correlation is for Bi and Cd elements, respectively. Accordingly, it can be concluded that the studied heavy metals have a spatial structure and are distributed in cluster form. In other words, the data tend to be concentrated in study area and have been influenced by almost the same factors. The results of the local Moran’s I analysis showed that the Bi and Pb have the highest and lowest high-high points, respectively, and the Co and Pb have the highest and lowest low-low points, respectively. According to the local Moran’s I statistics, the most polluted region of the study area was detected in the western part of the Baycheh-Bagh mine which are located on the polymetallic vein-veinlet mineralizations and related alterations. These metals include As, Bi, Cd, Co, Sb, Zn and Pb which have sheared between high-high points. The analysis of the samples from the stream sediments shows that the source of the concentration of the studied elements is geogenic (resulted from geological processes) and is related to mineralizations and alterations.

Collected geochemical data from stream sediments, can be used in regional exploration and identifying anomalies in reconnaissance stages. In this research in order to regional exploration studies, multifractal modeling approaches include concentration-area and concentration-number has been used and geochemical anomalies for index elements (As,Sb,Au and Cu) has examined. 855 of stream sediment samples were collected The Alut 1:100,000 sheet and analyzed by ICP-MS method in the laboratory of Geological Survey of Iran (GSI). Then, statistical parameters and histograms were performed on the elements. Then, using fractal methods concentration-area and concentration-number, related anomalies in this sheet has prepared and anomaly maps were drawn. Respect to the Geological setting, existing structures and predominant lithology the results of two methods (concentration - area and concentration – number) has compared in the area. The results of the two methods showed that concentration of these elements has increased in central and southeast regions and formed promising areas. Although concentration-number method due to more extensive geochemical halo included well-known deposits (Barika mine) and also accommodate expected mineralization in Sanandaj - Sirjan zone.

Fyrouzeh mine is located about 55 km northwest of Nyshabour in the Provice of Khorasan Razavi. The exposed rocks are mainly volcanic and intrusive with intermediate composition and all of them are altered. This mine is the first type of IOCG reconized in Iran with Cu-Au-LREE-U. Besides Cu-Au-U, this area shows As, Mo, Zn and Th anomalies. Geochemical evaluation of stream sediment with regard to environmental concern revealed high Cu anomalies.  Rocks show high uranium anomalies (up to 35 ppm) higher than the standard values (1 ppm). Airborne radiometric maps show high U and Th anomalies in a broad area. Ag, Hg and Mn show anomalies within the stream sediments. Cu, Pb, Zn, Ag, Ni, Mn, Sb, Hg, and U content of both drinking and agricultural water are fourtunatly within the range of standard, only two samples have higher As content (more than 10 ppb).  High level of U-Th radiation and contamination of stream sediment with respect to Cu, Hg, Ag, Mn and agricultural water to As are important environmental issues and people health therefore they need to be study.

Kalijar area is located in the North of Natanz in Isfahan Province. A number of igneous rocks have been occurred in two stages in this region. The first stage of volcanic rocks is include andesite bearing biotite, andesite bearing amphibole and green colour toffs (Eocene- Miopeliocene) and the second stage of plutonic rocks is include diorite, granodiorite bearing - hornblend and quartz monzonite (Oligo-Miocene) age in the area. The several alteration types have occurred in the area such as the sericitic, argillic and propylitic (chloritic and epidotic) that they are proximal to the fault units. The current alteration of index minerals are characterized by XRD analysis. Based on this approach, they are include calcite, quartz, alkali feldspar (Na-Ca), mica, hematite, dolomite and clay minerals. Geochemical exploration of stream sediments and heavy mineral methods were used to explore gold and copper mineralization in the area, which in the first stage 28 geochemical and 11 heavy mineral samples were taken and 68 geochemical and 18 heavy mineral samples in the second stage. The results which are gained by lab analysis by samples by ALS Chemex in Canada in ICPMS method to determine for rock forming and mineralizing minerals revealed the anomaly of Zn, As, W, Cu, Mo, Au, Ag, Pb elements in the area. The Spearman correlation coefficients has revealed the highest correlation between Fe,V(0.94), Pb,Zn (0.76), Mo,W(0.75), Cu,AS- (0.60) and W,Cr (0.81). Gold has shown the magximum correlation to Tungsten (0.54). Gold low correlation to the other metals, no correlation to rock forming minerals, represent the independent distribution of this element. Cu, Fe, Pb, Au have shown anomaly in heavy mineral studies. Nt-11, 35 ppm and Nt-12, 20 ppm of gold sampling have been harvested in this area, Two samples have been harvested from diorite mass borders (tuff rhyodacite unit) and andesite trachyte dyke to porphyrite, respectively. Geochemical anomaly maps indicates the highest gold concentration in south and the highest copper concentration in north. So they are possibly the best option for choosing the possible gold and copper mineralization. Gold mineralization to argillic alteration, copper mineralization to propylitic alteration had been shown on the basis of anomaly geochemical mineralization study. Gold and copper hydrothermal mineralization and their alteration association are related to hydrothermal solution in intrusive diorite mass (Upper Oligocene) age in northern area.

Abbas Abad area has an old copper mining history; in this area outcrop of volcanosedimentary sequences exist; lithological composition of volcanic parts are generally andesite and trachyandesite and sedimentary parts includes sandstone, limestone, conglomerate and shale. Mineralization in this area has occurred in a broad region (
35 Km2) in volcanic rocks with porphyry to megaporphyry texture. For surveying of arsenic distribution in this area chemical analysis on 52 samples of stream sediments near deposits located in north and northeast part of Abbas Abad (including Damanjala, Madan Bozorg, Asiadiv and Lab-e-Kal deposits) were done. Arsenic distribution, according to broad mineralization and old mining history were stndied. Arsenic distribution map shows the highest concentration of arsenic is in north east of the region; also using arsenic contents of stream sediments, background,threshold and anomaly values of arsenic determind which are 16 ppm, 21 ppm and 33 ppm respectively.